1. Field of Invention
This invention relates to a compact and inexpensive differential pressure measurement apparatus having a simple structure and which can be manufactured without any special pressure resistant casing or any protective mechanism against overpressure, and which is free of pressure-resistant hermetic terminals.
The invention also relates to a semiconductor type differential pressure measurement apparatus comprising a measuring diaphragm provided on both sides thereof with two measuring chambers each having a predetermined spacing such that it may be immediately stopped by the wall of the measuring chamber when an overpressure is applied to the measuring diaphragm; and which directly utilizes the strain detector for measuring the pressure difference as the detector element for overpressure; and therefore the invention is a simple and inexpensive semiconductor type differential pressure measurement apparatus which is highly reliable for detecting overpressure.
The invention further relates to a semiconductor type differential pressure measurement apparatus manufacturing method which is inexpensive and can manufacture diaphragms with highly precise thicknesses.
The invention also relates to a method for manufacturing a semiconductor type differential pressure measurement apparatus by utilizing a sacrificial layer etching method to eliminate the possibility of the diaphragm adhering to the substrate.
2. Description of the Prior Art
FIG. 1 is an explanatory drawing of a prior art structure, such as shown, for example, in JP-A-59-56137, a published unexamined Japanese application.
Referring to FIG. 1, a flange 2 and another flange 3 are fitted and assembled on both sides of a housing 1 by means of welding or the like, and an inlet 5 for introducing a high pressure fluid with a pressure of P.sub.H and an inlet 4 for introducing a low pressure fluid with a pressure of P.sub.L are provided on both flanges 2 and 3. A pressure measuring chamber 6, provided with a center diaphragm 7 and a silicon diaphragm 8, is provided inside housing 1.
Center diaphragm 7 and diaphragm 8 are each separately fixed on the wall of the pressure measuring chamber 6, to divide chamber 6 into two parts. Plates 6A and 6B are provided on the wall of the pressure measuring chamber 6 in such a manner that they face center diaphragm 7. The periphery of center diaphragm 7 is welded to housing 1.
Diaphragm 8 is made entirely from a single crystal substrate. Four strain gauges 80 are formed on one side of a silicon substrate by selective diffusion of an impurity such as boron, and the other side is subjected to machining and etching to form a concave diaphragm. When diaphragm 8 is subjected to a differential pressure .DELTA.P, two of the strain gauges 80 are subjected to tension whereas the remaining two gauges undergo compression. The strain gauges are connected to a Wheatstone bridge to detect the change of differential pressure .DELTA.P as a change in electric resistance. A lead 81 is attached at one end to the strain gauge 80, and is connected to a hermetic terminal 82 at the other end.
The hermetic terminal 82 is held by a support 9. The end of support 9 facing pressure measuring chamber 6 is fixed and adhered to diaphragm 8 using a low melting point glass or the like.
Pressure introducing chambers 10 and 11 are provided between housing 1 and each of flanges 1 and 2. Liquid separation diaphragms 12 and 13 are further provided inside pressure introducing chambers 10 and 11, and back plates 10A and 11A having shapes similar to liquid separation diaphragms 12 and 13 are formed on the wall of housing 1 in such a manner that they face liquid separation diaphragms 12 and 13.
Liquid separation diaphragms 12 and 13 together with back plates 10A and 11a define a space communicating with pressure measuring chamber 6 via communicating holes 14 and 15. Portions 101 and 102 filled with a sealed liquid such as silicon oil are provided between liquid separation diaphragms 12 and 13 in such a manner that the sealed liquid may reach the upper and lower planes of diaphragm 8 through communicating holes 16 and 17. The sealed liquid is separated into portions 101 and 102 by center diaphragm 7 and silicon diaphragm 8 such that the amounts in both are substantially equal.
The foregoing apparatus allows transmission of a pressure being exerted from the high pressure side, by transmitting the pressure applied to liquid separation diaphragm 13, to silicon diaphragm 8 via sealed liquid portion 102. When a pressure is applied from the low pressure side, on the other hand, the pressure applied to liquid separation diaphragm 12 is transmitted to silicon diaphragm 8 via sealed liquid portion 101.
Accordingly, it can be seen that silicon diaphragm 8 is deformed by the pressure difference between the pressure on the high pressure side and that on the low pressure side. This quantity of deformation, i.e., strain, is electrically detected by strain gauge 80 for measuring the differential pressure.
The foregoing apparatus, however, suffers from the following disadvantages. (1) Because the pressure P.sub.H on one side of the apparatus is applied to the periphery of the sensor, the exterior of the sensor must be covered by a pressure resistant container. (2) A pressure resistant hermetic seal terminal for transmitting the detected electrical signal to the outside is required. (3) A complex manufacturing method is required to produce a sensor, because a silicon wafer must have both faces thereof machined. (4) An overpressure protection mechanism should be provided separately because the sensor alone has no such protective means against overpressure.